(57) There is provided a pacemaker system with an SRD detection and intervention feature,
which enables a simple way of initiating confirmation of SRD, i.e., looking for an
AS/AP transition in a DDD or DDI pacemaker, or a transition from a VS to a VP in a
DDI pacemaker. This simple initiation of SRD confirmation is made possible by use
of a relatively wide hysteresis band which is normally operative when a spontaneous
rate is present, and which tracks physiological changes in the patient's natural rate,
across the pacemaker rate range. Transitions which result from a gradual decrease
in natural rate and thus represent physiological bradycardia are not interpreted as
suggesting SRD. The detection is confirmed only after a predetermined number of pace
pulses are delivered at the hysteresis rate, i.e., 1-5 pulses. In a preferred embodiment,
after confirmation of SRD, pacing starts at a programmable intervention rate, and
rate flywheels downward toward a lower rate limit, with intermittent hysteresis scans
at a lower rate to enable recovery of an underlying natural rate. The SRD mode is
left whenever recovery of a natural rate is confirmed, as by sensing a predetermined
number of consecutive natural atrial beats in DDD mode or atrial and/or ventricular
beats in DDI mode.
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